Λ-doublet and spin-doublet population distributions in the products of photofragmentation via coupled electronic channels: H2O(B 1A1)→H+OH(X 2Π)

The consequences of the photofragmentation of a triatomic molecule on several coupled potential energy surfaces are considered with specific attention to branching ratios over the fine structure components of an open-shell product with orbital degeneracy. Attention is limited to the cases where the parent molecule dissociates on singlet surfaces. It is shown how the components of the outgoing wave function on the different surfaces interfere in determining these ratios. The theory is applied to the dissociation of H2O through its second B̃ 1A1 excited state, for which the coupling between three singlet states of the parent (B̃, Ã, and X̃) leads to two sets of dissociation products, H+OH(X 2Π) and H+OH(A 2Σ+). The variation with N of the Λ-doublet ratios in the OH(X) state is found to be a very sensitive function of the quantum state of the parent molecule, of the energy, and of the exit channel potentials.